Spectro-imagery of an active tornado-like prominence: formation and evolution

Abstract

Context. The dynamical nature of fine structures in prominences remains an open issue, including rotating flows in tornadoprominences. While the Atmospheric Imaging Assembly (AIA) imager aboard the Solar Dynamics Observatory (SDO) allowed us to follow the global structure of a tornado-like prominence during five hours, the Interface Region Imaging Spectrograph (IRIS), and the Multi subtractive Double pass spectrograph (MSDP) permitted to obtain plasma diagnostics of its fine structures. Aims. We aim to address two questions. Is the observed plasma rotation conceptually acceptable in a flux rope magnetic support configuration with dips? How is the plasma density distributed in the tornado-like prominence? Methods. We calculated line-of-sight velocities and non-thermal line widths using Gaussian fitting for Mg ii lines and bisector method for Hα line. We determined the electron density from Mg ii line integrated intensities and profile fitting methods using 1D NLTE radiative transfer theory models.Results. The global structure of the prominence observed in Hα, and Mg ii h and k lines fits with a magnetic field structure configuration with dips. Coherent Dopplershifts in red-and blue-shifted areas observed in both lines were detected along rapidly-changing vertical and horizontal structures. However, the tornado at the top of the prominence consists of multiple-fine threads with opposite flows suggesting counter streaming flows rather than rotation. Surprisingly we found that the electron density at the top of the prominence could be larger (10 11 cm −3 ) than in the inner part of the prominence. Conclusions. We suggest that the tornado is in a formation state with cooling of hot plasma in a first phase, and following that, a phase of leakage of the formed blobs with large transverse flows of material along long loops extended away of the UV prominence top. The existence of such long magnetic field lines on both sides of the prominence would avoid the tornado-like prominence to really turn around its axis.

Solar prominence diagnostics from non-LTE modelling of Mgii h&k line profiles

“…The Hinode observations consisted of X-Ray Telescope (XRT; Golub et al 2007) observations with three filter combinations, Al poly/Open, Open/Gband, and Open/Ti with an FOV of 263.3 ×263.3 , centred on helioprojective coordinates 607.2 , -749.7 . The MSDP observations start at 12:05 UTC and end at 16:35 UTC with a reconstructed FOV of 270 ×370 (see Barczynski et al 2021). AIA whole-disc observations were also available.…”